Littérature scientifique sur le sujet « Abstract, concrete, neural substrate, anesthesia »

Viewing of single words produces a cognitively complex mental state in which anticipation, emotional responses, visual perceptual analysis, and activation of orthographic representations are all occurring. Previous PET studies have produced conflicting results, perhaps due to the conflation of these separate processes or the presence of subtle differences in stimulus material and methodology. A PET study of 10 normal individuals was carried out using the bolus H215O intravenous injection technique to examine components of processing of passively viewed words. Subjects viewed blocks of random-letter strings or abstract, concrete, or emotional words (words with positive or negative emotional salience). Baseline conditions were either passive viewing of plus signs or an anticipatory state (viewing plus signs after being warned to expect words or random letters to appear imminently). All words (and to a lesser extent the random letters) produced robust activation of cerebral blood flow in the left posterior temporal lobe, in addition to bilateral occipital activation. Furthermore, emotional words produced activation in orbital and midline frontal structures. Further activation in the left orbital frontal gyrus, the left inferior temporal gyrus, the left caudate nucleus, the anterior cingulate, and the cerebellum could be ascribed to the anticipatory state. This pattern of activity suggests that the occipital regions are recruited for visual-perceptual analysis of words, and the left temporal lobe represents the neural substrate for the orthographic lexicon. In addition, emotionally relevant material produces further processing in limbic brain structures of the frontal lobes. Detailed analysis of the task therefore substantially clarifies the neuroanatomic basis of single-word processing.

A view is put forward, according to which various aspects of the structure of the world as internalized by the brain take the form of “neural spaces,” a concrete counterpart for Shepard's “abstract” ones. Neural spaces may help us understand better both the representational substrate of cognition and the processes that operate on it. [Shepard]

This paper considers three classes of analyses of the nature of consciousness: abstract theories of the functional organization of consciousness, and concrete proposals as to the neural substrate of consciousness, while providing a rationale for contesting non-neural and transcendental conceptualizations of consciousness. It indicates that abstract theories of the dynamic core of consciousness have no force unless they are grounded in the physiology of the brain, since the organization of dynamic systems, such as the Sun, could equally well qualify as conscious under such theories. In reviewing the wealth of studies of human consciousness since the mid-20th century, it concludes that many proposals for the particular neural substrate of consciousness are insufficient in various respects, but that the results can be integrated into a novel scheme that consciousness extends through a subcortical network of interlaminar structures from the brainstem to the claustrum. This interstitial structure has both the specificity and the extended connectivity to account for the array of reportable conscious experiences.

Abstract The goal of the present paper is to provide an embodied cognitive science view on representation. Using the fundamental task of category learning, we will demonstrate that this perspective enables us to shed new light on many pertinent issues and opens up new prospects for investigation. The main focus of this paper is on the prerequisites to acquire representations of objects in the real world. We suggest that the main prerequisite is embodiment which allows an agent - human, animal or robot - to manipulate its sensory input such that invariances are generated. These invariances, in turn, are the basis of representation formation. In other words, the paper does not focus on representations per se, but rather discusses the various processes involved in order to make learning and representation acquisition possible. The argument structure is as follows. First we introduce two new perspectives on representation, namely frame-of-reference, and complete agent. Then we elaborate the complete agent perspective and focus in particular on embodiment and situatedness. We argue that embodiment has two main aspects, a dynamic and an information theoretic one. Focusing on the latter, there are a number of implications: Representation can only be understood if the embedding of the neural substrate in the physical agent is known, which includes morphology (shape), positioning and nature of sensors. Because an autonomous mobile agent in the real world is exposed to a continuously changing high-dimensional stream of sensory stimulation, if it is to learn category distinctions, it first needs a focus of attention mechanism, and then it must have a way to reduce the dimensionality of this high-dimensional sensory stream. Learning is very hard because the invariances are typically not found in the sensory data directly - the classical problem of object constancy: it is a so-called type 2 problem. Rather than trying to improve the learning algorithms - which is the standard approach - the embodied cognitive science view suggests a different approach which focuses on the nature of the data: the agent is not passively exposed to a given data distribution, but, by exploiting its body and through the interaction with the environment, it can actually generate the data. More specifically, it can generate correlated data that has the property that it can be easily learned. This learnability is due to redundancies resulting from the appropriate interactions with the environment. Through such interactions, the former type 2 problem is transformed into a type 1 problem, thus reducing the complexity of the learning task by orders of magnitude. By observing the frame-of-reference problem we will discuss to what extent these invariances are reflected - represented - in the “neural substrate”, i.e. the internal mechanisms of the agent. It is concluded, that representation is not a concept that can be studied in the abstract, but should be elaborated in the context of concrete agent-environment interactions. These ideas are all illustrated with examples of natural agents and artificial agents. In particular, we will present a suite of experiments on simulated and real-world artificial agents instantiating the main arguments

Abstract Background Social deficits are a well-known phenotype of schizophrenia, which strongly influence the clinical progress of patients. A core substrate of these dysfunctions are altered Theory of Mind (ToM) processes which critically shape social interactions and can impress in an exaggerated and atrophied form in the disorder. Although there is a well-established link between clinical outcome measures and ToM deficits, less evidence exists about the neural and behavioral mechanisms underlying a specific core function responsible for forming interpersonal mental representations, which in turn aid to optimize social interactions. Along this line, an urgent clinical issue is how alterations in these interpersonal predictive processes translate into clinical issues and whether they can be positively influenced by psychological group interventions. Methods In a set of different studies, we used functional and structural magnetic resonance imaging and a dynamic social interactive task, a modified prisoner’s dilemma game, in which the participants can form mental representations of different interaction partners in order to optimize their joint interaction sequences. Methodologically, we have drawn on several sophisticated methods ranging from graph theoretic network indices, functional and effective connectivity to structural covariance analyses and linked them with behavioral and clinical outcome measures. Results Our data shows a central relevance of the right temporo-parietal junction (rTPJ) in forming mental representations in healthy subjects, given the region integrates memory processing streams during social interactions. Further behavioral analyses indicate that these mechanisms are relevant for interpersonal adaptive processes during social interactions. In patients with schizophrenia, we have found dysfunctions in this important mechanism, indicated by a reduced integration of neural pathways from the temporal lobe, such as the hippocampus. These alterations are associated with behavioral indices of dysfunctions in generating mental representations during an interpersonal interaction. When we examined neural computations in the entire ToM network, we found for the first time that the rTPJ has reduced out-going effective connections to brain regions linked with higher-order cognition, such as the dmPFC, in patients. On a conceptual level, this finding might be associated with dysfunctional updating processes from brain regions located in the temporal lobe, which will be an ongoing empirical question. Discussion Our results indicate a central pathological relevance of the rTPJ for social dysfunctions in schizophrenia. First, the regions seem to be less informed by memory processing streams, relevant to update social information by previous information. Additionally, we have shown that in the core mentalizing network the region integrates to a lesser extent into the dmPFC, which might be associated with our previous findings. Our results show concrete targets for specific interventions to improve the clinical important social-cognitive dysfunctions occurring in the disorder. Hence, we suggest approaches to enhance the functioning of brain mechanisms relevant for human connections that can facilitate the patients’ clinical outcome.

There is evidence that abstract and concrete words are represented and processed differently in the brain. Numerous studies suggest the activation of a bilateral network for both abstract and concrete words, with a greater involvement of posterior, sensory areas in concrete word processing, and a more focal activation of anterior regions, involved in verbal processing, for abstract words. This Ph.D. thesis aimed at investigating the different neural substrates of concrete and abstract words by studying memory priming during general anesthesia. Implicit memory tasks, in fact, seem to be immune to the concreteness effect and recent neurophysiological studies suggest that conscious and unconscious semantic activation involve similar brain areas. Experiment 1 focused on the priming effect for intraoperatively primed abstract and concrete words in patients under general intravenous (propofol) anesthesia. Considering the specific brain targets of propofol, I hypothesized a stronger priming effect for concrete than for abstract words. Implicit memory for primed words was tested with a three-letter word stem completion test, in which half of the stems referred to primes, and half were foils. Both stimulation and testing were auditory, to avoid cross-modality interference. A control group of patients, who did not receive any intraoperative stimulation, but completed both concrete and abstract word stem completion test, was also recruited. As expected, a priming effect was found for concrete words, since the number of target hits was significantly higher than the number of non target hits. This difference did not apply to abstract words. The abstract experimental group performed comparably to controls. These results support the thesis that abstract word processing relies on the activity of anterior brain areas, as for example the inferior frontal cortex, which are suppressed by propofol. The results would also confirm that priming, investigated through word stem completion, is not a simple perceptual, pre-semantic task, but engages multiple processes, including semantic access. As suggested by electrophysiological studies, semantic access might occur at very early stages of verbal processing, thus explaining a selective intraoperative priming effect for concrete words only. To further investigate these hypotheses, a second experiment was conducted. In experiment 2 the same methodology of experiment 1 was applied, but the volatile anesthetic sevoflurane was used, which is known to lower activity in brain regions located more posteriorly than those suppressed by propofol. The most interesting finding was the presence of a priming effect also for abstract words, which would confirm data from neuroimaging studies of a greater engagement of anterior brain regions in abstract word processing. To better define the involvement of the frontal cortex in the processing of abstract words, a series of patients undergoing awake surgery for brain tumor removal was studied in experiment 3. Patients performed a lexical and a semantic decision task, together with a standard intraoperative cognitive monitoring, during direct cortical stimulation. The fundamental role of the left inferior frontal gyrus in abstract word processing was confirmed.